1. Field of the Invention
The present invention relates to an integrated image processing apparatus for processing image data scanned by a scanner in a digital scanner, a digital copying machine or a facsimile machine, and more particularly to an integrated image processing apparatus for reducing image noise on image data that is of low density and low contrast so that image characters are reproduced well on their background.
2. Discussion of the Background
Image data scanned by a scanner in a digital scanner, a digital copying machine or a facsimile machine is usually processed, for example, in a dither process for a photograph image, a moire deducing process for halftone images or an MTF (Modulation Transfer Function) compensation process for line images.
In case an original image is mixed with a fine line image, e.g., a character, and a halftone image, e.g., a photograph, another process to find an edge of the image is required. One of the known processes is shown as Japanese Patent Application (KOUKOKU) 6-14352. In this process, the edge of image is found by binary data converted using a cut-off level.
Another background image processing apparatus is shown as Japanese Laid-Open Patent Application (KOKAI) 4-220080. In this process, the cut-off level can be changed by an average of the image data.
In the foregoing image processing apparatuses, a binary cut-off level is established for discriminating between a character (black region) and a background (white region). However, as the cut-off level is fixed, the problem arises that the quality of the reproduced image depends on the quality of the original image. For example, the background of the character may be dark or there may be a white blank or an isolated black speck, which may cause the fixed cut-off level to produce erroneous output.
In case of combining known image processing techniques, there arise problems of complicating the structure of the apparatus used, or slowing down the speed of the process.